*{
    margin: 0;
    padding: 0;
    list-style: none;
}
nav{
    width: 300px;
    height: 200px;
    margin:auto;
    background-color: saddlebrown;
    margin-top: 200px;
}
.ul{
    display: flex;
}
.ul li{
    margin: 10px;
    border: 1px solid aqua;
}
.huadong div{
    background-color: seagreen;
    margin-top: 20px;
    display: none;
}
.huadong div a{
    font-size: 14px;
    margin: 6px;
}
.huadong .chuxian{
    display: block;
}